1. Field of the Invention
The present invention relates to a liquid discharge method for discharging desired liquid by bubble generation induced by applying thermal energy to liquid, a liquid discharge head and a liquid discharging apparatus utilizing such liquid discharge method, and particularly to a liquid discharge method employing a movable member displaced utilizing the bubble generation, and a liquid discharge head and a liquid discharge apparatus utilizing such liquid discharge method.
The present invention is applicable also to an apparatus for example a printer for recording on a recording medium such as paper, yarn, fiber, cloth, leather, metal, plastics, glass, wood or ceramics, a copying apparatus, a facsimile apparatus having a communication system, or a word processor having a printer unit, or to an industrial recording apparatus combined in complex manner with various processing apparatus.
In the present invention, recording means not only providing the recording medium with a meaningful image such as a character or graphics but also with a meaningless image such as a pattern.
2. Related Background Art
There is already known so-called bubble jet recording method, or an ink recording method in which for example thermal energy is given to liquid ink contained to generate a state change involving a rapid volume change (generation of a bubble) therein, and the ink is discharged from a discharge port by an action force based on such state change and is deposited on a recording medium to form an image. The recording apparatus utilizing such bubble jet recording method is generally provided, as disclosed in the U.S. Pat. No. 4,723,129, with a discharge port for discharging ink, an ink flow path communicating with the discharge port, and an electrothermal converting member constituting energy generation means for discharging ink contained in the flow path.
Such recording method, being capable of recording a high quality image at a high speed with a low noise level and also of arranging the discharge ports for ink discharge at a high density in the recording head for executing such recording method, has various advantages such as ability to recording an image of a high definition with a compact apparatus and to record a color image easily. Such bubble jet recording method is recently employed in various office equipment such as a printer, a copying apparatus, a facsimile apparatus etc. and even to industrial systems such as a print dyeing apparatus.
With such spreading of application of the bubble jet technology, there are being generated various requirements as explained in the following.
For obtaining an image of high quality, there are proposed a driving condition for realizing a liquid discharge method capable of providing a high ink discharge speed and achieving satisfactory ink discharge based on stable bubble generation, and an improved shape of the flow path for obtaining a liquid discharge head with a high liquid refilling speed into the flow path, in view of the high speed recording.
In addition to such head structures, the Japanese Patent Application Laid-Open No. 6-31918 takes into consideration a backward wave (pressure generated in a direction opposite to that toward the discharge port) and discloses a structure capable of preventing the backward wave causing an energy loss at the ink discharge (specifically in FIG. 3 of the same patent application). In the liquid discharge head disclosed in the above-mentioned patent application, a triangular portion of a triangular plate-shaped member is positioned opposed to the heater for generating the bubble. In such liquid discharge head, the backward wave is temporarily and slightly suppressed by the plate-shaped member, but the relationship between the bubble growth and the triangular portion of the plate-shaped member is not at all disclosed nor considered, so that the above-mentioned liquid discharge head has the following drawbacks.
In the above-mentioned patent application, the shape of the liquid droplet cannot be stabilized since the heater is positioned in the bottom of a recess and is not in linear communication with the discharge port and the bubble growth from a side of the triangular plate-shaped member to the entire other side since the bubble growth is permitted from the vicinity of the apex of the triangular portion, whereby the bubble executes ordinary growth in the liquid as if the plate-shaped member is not present. Consequently the presence of the plate-shaped member does not affect at all the grown bubble. Inversely, since the plate-shaped member is entirely surrounded by the bubble, the liquid refill to the heater position at the bottom of the recess generates a random flow at the contraction of the bubble, thereby resulting in accumulation of small bubbles in the recess and disturbing the liquid discharging principle itself based on the bubble growth.
On the other hand, the EP laid-open No. 436047A1 discloses an invention of alternately opening a first valve for intercepting a path between an area in the vicinity of the discharge port and a bubble generating portion and a second valve for intercepting a path between the bubble generating portion and an ink supply portion (cf. FIGS. 4 to 9 in the EP laid-open No. 436047A1). In such invention, however, since only two of the three chambers are separated at a time, the ink discharged following the ink droplet forms a large trailing, whereby a satellite dots considerably increase in comparison with the ordinary liquid discharge method executing the bubble growth, bubble contraction and bubble vanishing. This is presumably because the effect of meniscus retraction by the vanishing of bubble cannot be utilized. Also at the liquid refilling, the liquid is supplied to the bubble generating portion by the bubble vanishing, but cannot be supplied to the area in the vicinity of the discharge port until a next bubble is generated, so that such liquid discharger head not only shows a large fluctuation in the discharged liquid droplet but also has a very low response frequency of liquid discharge, thus being not in the practical level.
Also there have been made various proposals on a liquid discharge head different completely from the aforementioned liquid discharge head and having a movable member capable of effectively contributing to the liquid discharge droplet (for example a plate-shaped member of which a free end is positioned closer than the fulcrum thereof to the discharge port). Among such proposals, the Japanese Patent Application Laid-Open No. 9-48127 discloses a liquid discharge head capable of limiting the upper limit of displacement of the aforementioned movable member, in order to prevent a slight aberration in the behavior of such movable member. Also the Japanese Patent Application Laid-Open No. 9-323420 discloses a liquid discharge head in which the position of a common liquid chamber, formed at the upstream side of the aforementioned movable member, is shifted to the free end side thereof, namely to the downstream side, utilizing the advantage of the movable member, thereby improving the refilling ability. Since these inventions have been based on a concept that the growing bubble, temporarily retained by the movable member, is suddenly released toward the discharge port, the various factors of the entire bubble relating to the liquid droplet formation and the mutual relationships of such factors have not been considered.
As a next step, the Japanese Patent Application Laid-Open No. 10-24588 discloses an invention of releasing a part of the bubble generating area from the aforementioned movable member, in consideration of the bubble growth by propagation of the pressure wave (acoustic wave) as a factor relating to the liquid discharge. However, also this invention considers only the bubble growth at the liquid discharge, so that the various factors of the entire bubble relating to the liquid droplet formation and the mutual relationships of such factors have not been considered.
Also it is already known, in the liquid discharge head of edge shooter type (a head having the discharge port in a direction parallel to the heater forming plane), that a frontal portion (portion close to the discharge port) of the bubble generated by film boiling significantly influences the liquid discharge, but there has not been considered to utilize such portion for more effectively forming the liquid droplet to be discharged, and the present invention has been reached as a result of intensive investigation for technically clarifying these factors.
In addition, in the most of prior art, plural heat generating member are selectively driven to modulate a discharge amount or perform multi-value gradation recording. Such structure has a difficulty in disposing each of plural heat generating members to an optimum position and in making a head compact.
The present invention is one of those reached in the course of detailed analysis of the process from the generation of the bubble to the extinction thereof, and has attained a technical level much higher than the prior technology, in realizing multi-value gradation recording and attaining stable image quality in the continuous discharge operation.
The principal objects of the present invention are as follows.
A first object of the present invention is to provide an extremely novel liquid discharge principle by controlling the generated bubble and the liquid at the discharge port side and at the supply side of the bubble by a movable member and a structure of the entire liquid flow path.
A second object of the present invention is to unite plural discharged liquid droplets in continuous discharging operation and to cause such united droplet on a recording medium, thereby enabling to control the discharge amount of the liquid droplet discharged from a same nozzle and realizing recording of multi gradation levels.
A third object of the present invention is to provide a liquid discharge apparatus capable of attaining high speed recording and high image quality at the same time.
The above-mentioned objects can be attained, according to the present invention, by a liquid discharge method consisting of heating liquid in a liquid flow path to generate and grow a bubble in the liquid, displacing a movable member formed as a beam supported at an end thereof and provided in the liquid flow path from an initial state according to the growth of the bubble, thereby suppressing the flow of the liquid toward the upstream side of the liquid flow path and the growth of the bubble, discharging the liquid as a droplet from a discharge port communicating with the downstream side of the liquid flow path by the pressure resulting from the growth of the bubble, and, after the discharge of the liquid droplet, returning the movable member from the displaced state to the initial state according to the extinction of the bubble, wherein, in case of executing continuous liquid discharge from the same liquid flow path, the heating of the liquid for the next liquid discharge is initiated before the vibration of the movable member returning from the displaced state after the preceding liquid discharge completely converges and while the movable member displaced to the initial position, thereby discharging plural liquid droplets in continuous manner from the same discharge port and whereby the plural liquid droplets are united into a single liquid droplet before landing on the recording medium.
The aforementioned liquid discharge method is featured in that the movable member at the start of second or subsequent bubble generation is in a displaced state, and the displacement amount of the movable member (amount of movement of the movable member from the initial state to the displaced state) at the start of bubble generation is larger than the displacement amount of the movable member at the start of preceding bubble generation.
The aforementioned liquid discharge method is featured in that, in the continuous discharge of liquid droplets, the discharge speed of a succeeding liquid droplet is larger than that of a preceding liquid droplet.
In the aforementioned liquid discharge method, it is preferred that a heat generating member is provided in the liquid flow path and is driven to execute heading of the liquid. In such case, the heat generating member may be an electrothermal converting member which may be given a driving pulse to execute heating of the liquid.
According to the present invention, there is also provided a liquid discharge apparatus which is equipped with the aforementioned liquid discharge head and recording medium conveying means for conveying a recording medium for receiving the liquid discharged from the liquid discharge head, which executes recording by causing the liquid discharge head to discharge ink and depositing the ink onto the recording medium.
In the description of the present specification, the expression upstream or downstream is used with respect to the direction of flow of the liquid from a liquid supply source through a bubble generating area (or movable member) toward a discharge port or to the direction of such configuration.
Also the downstream side of the bubble itself means a bubble generated in an area at the downstream side in the aforementioned flow direction or configurational direction with respect to the center of the bubble or in an area of the heat generating member at the downstream side with respect to the aerial center thereof. Similarly, the upstream side of the bubble itself means a bubble generated in an area at the upstream side in the aforementioned flow direction or configurational direction with respect to the center of the bubble or in an area of the heat generating member at the upstream side with respect to the aerial center thereof.
Also in the present invention, substantial contact between the movable member and a limiting portion therefor may be a directly contacting state or a closely positioned state where liquid of a thickness of several micrometers is present between the two.